Ashlee Simpson’s triumphant tweet last month announcing her engagement to her “baby love,” Evan Ross, may have taken some by surprise.

But Ross’ big sister, Rhonda, says the family is ready and willing to embrace the union of diva Diana’s son with Jessica Simpson’s little sister.

“I’m really excited for the both of them,” Rhonda Ross, 42, told The Post after the Tracy Reese runway show on Sunday. “I’m really happy to have her join the family.”

Rhonda, the eldest of Diana Ross’ five children — and half-sister to Evan, son of the late Norwegian mountaineer and businessman Arne Naess Jr. — says the families came together to celebrate over the holidays.

“We just spent Christmas with Ashlee and her son, Bronx,” she said. “Ashlee’s son is the same age as my son, so they play together.”

The Harlem-based singer also told The Post that she is getting ready to release a new jazz album.

“My music is a mix of jazz, neo soul and a little funk in there. It’s jazz but it’s what I call accessible and danceable jazz.”